The present invention relates to wireless communication, such as provided by systems as specified in 3GPP (Third Generation Partnership Project) Wideband Code Division Multiple Access (WCDMA) release 5, High Speed Downlink Packet Access (HSDPA), but also as provided by other kinds of wireless communications systems providing for packet transmission. More particularly, the present invention relates to the paging of mobile stations communicating with a base station in such communication systems.
FIG. 1 illustrates a radio frame that includes a number of complex (in-phase and quadrature) chips divided among fifteen slots. The radio frame may have a duration of ten milliseconds (10 ms) and include 38400 chips. In the Third Generation Partnership Project (3GPP) each such frame is called a Transmission Time Interval (TTI) defining the periodicity at which Transport Block Sets are transferred to the physical layer on the radio interface. Each slot thus includes 2560 chips, which may represent, for example, ten 256-chip symbols (with an SF of 256). Such a frame/slot/chip structure is a feature of the 3GPP, wideband CDMA communication system currently under consideration. The radio signal transmitted by a BS in such a communication system is the sum of spread and scrambled data and control bits and an unscrambled synchronization channel. Data and control bits are typically spread by either bit-wise (in DS-CDMA systems) or block-wise replacement by an orthogonal sequence or sequences, such as Walsh-Hadamard sequences. (This is sometimes called m-ary orthogonal keying.) As noted above, the spread results are then scrambled usually by bit-wise modulo-2 addition of a pseudo-noise (PN) scrambling sequence.
It will be appreciated that the data bits include user information, such as audio, video, and text information, and that the information of different users is made distinguishable, in accordance with CDMA principles, by using distinguishable spreading sequences, such as mutually orthogonal Walsh-Hadamard sequences. In a sense, then, each user""s Walsh-Hadamard sequence(s) define that user""s communication channel, and thus these distinguishable sequences are said to channelize the user information. The construction of sequences according to their correlation properties is described in U.S. Pat. No. 5,353,352 to P. Dent et al for Multiple Access Coding for Radio Communications and U.S. Pat. No. 5,550,809 to G. Bottomley et al for Multiple Access Coding Using Bent Sequences for Mobile Radio Communications.
It is desirable to provide various types of communication services to meet various consumer demands, such as voice telephony, facsimile, e-mail, video, Internet access, etc. Moreover, it is expected that users may wish to access different types of services at the same time. For example, a video conference between two users would involve both voice and video support. Some services require higher data rates than others, and some services would benefit from a data rate that can vary during the communication.
FIG. 2 depicts a typical tree structure for Walsh-Hadamard sequences, or codes. Levels in the code tree define channelization codes of different lengths, corresponding to different spreading factors. In FIG. 2, the root of the tree is indicated by code C1,1 that has a spreading factor SF=1, level 1 of the tree includes codes C2,1 and C2,2 that each have spreading factors of 2, and so forth. At each level, exemplary corresponding sequences, or codes, are indicated. For the root level, the example shown is [1], for level 1, the example codes shown are [1 1] and [1 xe2x88x921], and so forth. In the notation Ck,i illustrated, k is the spreading factor SF and the index i simply distinguishes codes at the same level. It will be appreciated that the tree continues to branch as one moves to the right in FIG. 2 and that it is not necessary for the code sequence at the root level to have only one element as illustrated.
All codes in a code tree cannot be used simultaneously in the same cell or other environment susceptible to mutual interference because all codes are not mutually orthogonal; a code can be used if and only if no other code on the path from the specific code to the root of the tree or in the sub-tree below the specific code is used. This means that the number of available channelization codes is not fixed but depends on the rate and spreading factor of each channel in the group of channels that potentially can mutually interfere.
Eligible channelization codes can be allocated randomly from the available eligible codes in the code tree structure for channels of different rates and spreading factors, which is to say that the eligible codes may be allocated without co-ordination between different connections, other than maintaining orthogonality. On the uplink, different users (connections) use different scrambling codes, so all of the spreading codes in a tree can be used for each user without co-ordination among different users. The situation on the downlink could be different because the BS typically uses only one scrambling code for all users (connections). Thus, spreading codes cannot be allocated so freely; co-ordination among users is needed.
In WCDMA based systems high speed data transmission may be enabled, e.g., by means of the so called high speed downlink packet access (HSDPA) technology. The high speed downlink packet access (HSDPA) may include functions such as fast hybrid automatic repeat request (HARQ), adaptive coding and modulation (AMC) and/or fast cell selection (FCS). These functions are known by the skilled person and will thus not be explained in more detail. A more detailed description of these and other function of the HSPDA can be found, e.g., from a third generation partnership project technical report No. 3G TR25.848 release 2000 titled xe2x80x98Physical Layer Aspects of UTRA High Speed Downlink Packet Accessxe2x80x99. It shall be appreciated that although the HSDPA has been specified for use in the WCDMA, similar basic principles may be applied to other access techniques.
At the present it is assumed that in the high speed downlink packet access (HSDPA) each user equipment receiving data on a high speed downlink shared channel (HS-DSCH) also has an associated dedicated channel (DCH) allocated. The dedicated channel may be mapped to a dedicated physical channel (DPCH) in the physical layer. The DPCH is typically divided into dedicated physical data channel (DPDCH) and dedicated physical control channel (DPCCH) both in the uplink and the downlink. Data such as the power control commands, transport format information, and dedicated pilot symbols are transmitted on the DPCCH. Information such as diversity feedback information may also be transmitted on DPCCH in the uplink. The HS-DSCH may be mapped to one or several high speed physical downlink shared channels (HS-PDSCH) in the physical layer.
The associated dedicated channel is typically provided both in the downlink and the uplink. The dedicated channel is typically used to carry HSDPA related information/signaling as well as other dedicated data such as speech and control data. The user equipment may communicate with several base stations at the same time. For example, the associated dedicated channel may be in soft handover.
In addition to associated dedicated channels, the HS-DSCH may be associated also with a shared control channel (SCCH). The SCCH can be used to carry HS-DSCH specific information/signaling to those users receiving data on the HS-DSCH.
A current proposal is to use the dedicated channel to inform the user equipment that it has data to be read on the HS-DSCH and SCCH. That is, only those users receiving data at a given time will receive an indication on the dedicated channel. The dedicated channel may be called as a pointer channel since it points to the shared channels. The dedicated channel may also contain information about modulation and coding schemes, power levels and similar parameters used for the shared channels. This information can be sent also on the shared channel. The shared control channel on the other hand is used to carry information that is specific to the data transmitted on the shared data channel (HS-DSCH). This information can contain for instance packet numbers for the HARQ and so on. The shared control channel can be sent on a separate code channel (code multiplexed) or using the same code channels as HS-PDSCH (time multiplexed).
Unlike the dedicated channel, the HS-DSCH is assumed not to be in soft handover. That is, each base station is assumed to have their own shared channel and the user equipment is assumed to receive data from only one base station at a time. The so called fast cell selection (FCS) technique may be used to switch the data transmission from one base station to another. However, the shared channels does not use power control. Instead, the shared channels are proposed to be transmitted with fixed or semi-fixed power. The term xe2x80x98semi-fixedxe2x80x99 means in here that the power is not changed often. The power could, for instance, be a cell specific parameter.
In the currently proposed arrangements the high speed downlink shared channel (HS-DSCH) is planned to be associated with a dedicated channel which would carry in the downlink at least information regarding the timing when the receiving station is to receive on a shared channel. The associated dedicated channel may possibly carry also other information. In the uplink, the associated dedicated channel may carry, for example, the required acknowledgements (ACK) for a fast HARQ.
The Transmission Time Interval (TTI) for HSDPA will be shorter than for Rel""99 WCDMA. TTI lengths of 1, 3, 5 and 15 slots have been proposed, corresponding to 0.67 ms, 2 ms, 3.33 ms and 10 ms, respectively. Currently, 3 slots, i.e., 2 ms, TTI is most probable choice and is considered as preferred solution in this text.
In a packet access system, such as HSDPA, a user typically accesses the communication link (channel) and media only when the user has data to transmit or receive. In order to effectively utilize the communication link, several users usually share the same link.
So that each user knows when there is data to be received and so knows to access the communication link, in some systems a link master notifies the user that a data packet is about to be transmitted. Hence, in such systems, each user must more or less continuously listen to a packet paging channel.
Since a communication link can be statistically multiplexed between a large number of users, there would also be a multitude of packet paging channels required, one for each user. In order to make the number of paging channels as large as possible (i.e. in order to maximize the number of available codes and code channels), a spreading factor for the paging channel is used in some systems, and the spreading factor is made as high as possible so as to allow as many users as possible to use the same part of a code tree.
A high spreading factor for a paging channel implies a very low bit rate in the channel. On the other hand, a highly flexible and adaptive system, such as the proposed HSDPA, might require that a multitude of parameters be transmitted to a mobile station along with each packet.
For this reason, the prior art has proposed that another set of code channels, different from the paging channel, be used for parameter signaling. (When using another set of code channels for parameter signaling, the paging channel can also be called either a paging indicator channel or a pointer channel, since it either indicates that there is data to be received on the parameter signaling channel, or it points to a certain parameter signaling channel.) The number of such code channels should be the same as the number of code multiplexed users for any particular transmission interval. Since this number usually is much smaller than the number of active users, the prior art has proposed that the parameter signaling channels be shared among the active users. See for instance Chapter 6.3.2.1.2. (Two-step signaling approach) of 3GPP TR 25.855 v1.1.0.
As mentioned above, in HSDPA, a fixed spreading factor is used for the data code channels and at this time has a value of 16. Hence, there are at most sixteen full-speed data code channels available. At least one of the channels, i.e. one of the branches of the code tree, must be allocated for the common pilot channel (CPICH) used for instance for channel estimation in the mobile station and other common channels as well as for the dedicated (packet paging) channels and parameter signaling channels (also called shared control channels). The remaining fifteen code branches are, according to the prior art, temporarily allocated either to one user, or they are allocated to at most fifteen separate users. In the former case, one parameter signaling channel is needed; and in the latter case, fifteen parameter signaling channels are needed. Typically, the shared data channel is assumed to be shared within a given TTI by a number of users, which are code multiplexed. In FIG. 3, an example is shown with four shared control channels. In either case, there can be more than fifteen active users that share the data channels (via time division multiple access).
According to the prior art, each active mobile station decodes its own paging channel. When there is a transmission for a particular mobile station, the paging channel for the mobile station so indicates. In addition, the paging channel for the mobile station indicates the code (parameter signaling) channel where the parameters for the transmission interval are signaled. The mobile station then decodes the assigned parameter signaling channel, which enables the mobile station to then decode the actual data transmission.
The main problem with the above protocol is that if the paging channel content, parameter signaling channel content, and data channel(s) content are sent in sequence, then three frames or transmission time intervals (TTIs) are needed to complete one data transmission. The prior art therefore also provides that all of the content of all three different channels be sent simultaneously, i.e. in a single TTI.
If all of the content of all three different channels is sent simultaneously, the mobile station must buffer all channels that may have to be decoded, i.e. all the parameter signaling code channels and all the data channels; in the worst case for HSDPA, this amounts to a total of thirty separate channels. To provide a large enough buffer in the mobile station to handle thirty channels would be difficult and expensive. As an alternative to providing the buffer in the mobile station, the prior art also provides that the channels be despread and then buffered, rather than buffered on the chip level (i.e. before being despread, so that the channels are buffered with the spreading code, which requires more memory). Such an alternative requires less memory, but requires a larger number of despreaders.
What is needed, is a way to send to a mobile station the content of the three kinds of channels (the paging channel, the parameter signaling channel, and the data channel) without requiring as many despreaders as in the three-channel-at-a-time prior art, and without requiring three TTIs as in the one-channel-at-a-time prior art.
Accordingly, the present invention provides a packet-sending entity, such as a base station, and a packet-receiving entity, such as a mobile station, methods by which the packet-sending entity and packet receiving entity function so as to have the packet sending entity communicate a packet to the packet-receiving entity, and a corresponding system including both the packet-sending entity and the packet-receiving entity, the methods for use in a context in which the packet-sending entity and packet-receiving entity communicate via a packet communication system using a plurality of parameter signaling channels (SCCH), and also using a plurality of shared data channels (SDCH) and operating according to a protocol in which when packet data is to be transmitted from the packet-sending entity to the packet-receiving entity, the communication between the packet-sending entity and the packet-receiving entity occurs over one or more transmission time intervals (TTIs). The methods are such that once a parameter signaling channel is assigned to the packet-receiving entity for communicating a packet, the assigned parameter signaling channel is used by the packet-receiving entity in each subsequent TTI as long as there is at least a portion of the packet in the subsequent TTI, and when there is at least a portion of the packet in the subsequent TTI, for the subsequent TTI the packet-receiving entity despreads and decodes only one parameter signaling channel along with the data channels, and when there is not at least a portion of the packet in the subsequent TTI, for the subsequent TTI the packet-receiving entity despreads all the parameter signaling channels, and decodes either all, one, or none of the parameter signaling channels.
In a first aspect of the invention, a method is provided for operation of the packet-sending entity, the method including: a parameter transmitting step, having the packet-sending entity transmit to the packet-receiving entity at least some of the parameters for decoding some or all of the shared data channels using at least one of the parameter signaling channels; a data providing step, having the packet-sending entity provide to the packet-receiving entity the data to be communicated using at least one of the shared data channels according to the parameters provided on the at least one parameter signaling channel; and a further parameter transmitting step, having the packet-sending entity continue to use the same at least one parameter signaling channel to transmit parameters for decoding any additional data transmitted on at least one of the shared data channels for the same packet-receiving entity in the subsequent consecutive TTIs.
In a further aspect of the first aspect of the invention, in the parameter transmitting step, the packet-sending entity transmits to the packet-receiving entity within a TTI at least some of the parameters for decoding some or all of the shared data channels within the next TTI. In a still further aspect, in the data providing step, the packet-sending entity provides to the packet-receiving entity in the TTI immediately following the TTI in which the parameter signaling channel is transmitted the data to be communicated using at least one of the shared data channels according to the parameters provided on the at least one parameter signaling channel.
In a second aspect of the invention, a method is provided for operation of the packet-receiving entity, the method including the steps of: until the packet-sending entity assigns a parameter signaling channel to the packet-receiving entity, having the packet-receiving entity despread all the parameter signaling channels and decode a predetermined subset of the parameter signaling channels, wherein the predetermined subset of the parameter signaling channels is either all, one, or none of the parameter signaling channels; once a parameter signaling channel is first assigned to the packet-receiving entity, having the packet-receiving entity interpret the assignment to be an assignment of a parameter signaling channel for the current TTI, and having the packet-receiving entity despread and decode the assigned parameter signaling channel in the current TTI so as to obtain parameter data from the parameter signaling channel; having the packet-receiving entity use the parameter data in reading the content of the shared data channels in the subsequent TTI; having the packet-receiving entity monitor information communicated by the packet-sending entity so as to determine whether the next TTI includes at least a portion of the packet; in each TTI until the TTI prior to the last TTI in which a portion of the packet is transmitted over the data channels, having the packet-receiving entity despread only the assigned parameter signaling channel and also decode the assigned parameter signaling channel; and for the last TTI in which a portion of the packet is transmitted over the shared data channels, having the packet-receiving entity despread only the assigned parameter signaling channel and also buffer the assigned parameter signaling channel.
Thus, the invention provides a method and an arrangement to page a mobile station, a method and arrangement that minimizes the complexity of the mobile and maximizes the processing time of the base station if hybrid automatic repeat request (HARQ) is employed.